1. Field of the Invention
The present invention relates to maintenance holes in sewer systems, more commonly known as “manholes.” More particularly, it relates to a modular mold device and method of forming and engagement of components thereof providing great adaptability in the configuration of formed components therefrom employed in maintenance holes such as drain junctions, to provide a high degree of modularity and customization to a currently static art employing concrete with few options.
2. Prior Art
Maintenance holes (also known as utility holes, cable chambers, manholes, inspection chambers or access chambers) are employed through the world to provide access for workers and equipment to underground utilities such as sewers and drains or electrical utilities. Conventionally, such maintenance holes generally consist of a concrete shaft rising from a concrete base platform and a metal or plastic hole cover at the entry end of the concrete shaft.
In sewage and drainage systems, the base of the maintenance hole frequently serves as a common juncture or node for the many drain pipelines and conduits which typically network in a sanitary and/or storm sewer or drainage system. The inside of the shaft defining an axial chamber of the hole leading to the base is conventionally outfitted with steps or ladders which lead to the base. These steps, or handholds, allow workers to access the base and the junctions where a plurality of inlet and outlet openings are present. At these junctions, the pipes or conduits of drains communicate through the shaft and couple with the respective inlet and outlet pipes of the sewer systems.
Pipelines of such junction points can either pass through or join into one another in any number of combinations, at any number of angles, and pluralities. This affords the configurations of the bases of maintenance holes in such systems the potential to vary greatly from one base in the system, to another in the system. The respective required connection points and angles of intersection of the bases of maintenance shafts in conventional drainage systems can vary widely with every individual shaft and junction point since it is the angles of the incoming pipes or conduits which determine the configuration of the base.
Conventionally, maintenance hole shafts and bases are made from precast concrete or poured in-place concrete. Due to the nature of concrete, its drying times, and its weight and transportability limitations, the offering of different angles and types of interconnections available is slim. The cost to make, cure, stock and ship heavy precast concrete simply is not adaptable to a high degree of inventory and options being offered. Further, once concrete bases are formed, by the very nature of concrete, they are not easily changed or adapted to allow for any changing angles or new conduits communicating to the base.
With the potential current and future structure of the base varying to such a wide degree, tooling and manufacturing costs as well as functionality for precast concrete elements are also greatly affected. Furthermore, over time concrete being resistant to compaction, is also brittle if support is bent or strained and often requires rehabilitation or replacement due to degradation from earth settling and/or lateral movement caused by such settling or earth movements. Such degradation can also come from corrosive chemicals like sulfides, and in many areas of the country from environmental conditions such as freeze/thaw cycles, and water infiltration. Thus a small crack in a concrete formed base, caused by settling or lateral translation, can turn into a major structural defect when liquid enters the crack and freezes.
In addition to the ongoing potential for degradation of concrete bases, as noted, the precast concrete structures are difficult to transport due to the great weight and bulkiness of dried concrete. This weight and the careful nature in which concrete must be handled when transported to avoid cracking, makes it difficult for concrete formed bases and components to navigate down the narrow constraints of a maintenance hole shaft to the installation point.
All these factors combine in a symbiotic relationship which increases material and labor costs for such systems employing conventional concrete formed components. Additionally, environmental impacts such as increased green house gasses from the production and transport of concrete components themselves, diminish the sustainability of employing concrete over time.
Such serious pitfalls attributable to precast concrete for drain and sewer bases and tunnel liners have been rectified however, with the introduction of rigid plastics for plumbing and sewer and landscaping systems. These plastic counterparts are cost effective, require little to no maintenance, are non-toxic, and being lightweight they are easy to install.
For instance, U.S. Pat. No. 4,089,139 to Moffa et al. teaches a ‘segmented cylindrical reinforced plastic manhole structure’ adapted to support a conventional manhole cover. Moffa et al. consists of segmented cylindrical structure elements and a base element all cast or molded of reinforced plastic material. The base element however, is merely a cap, with pipeline inlet and outlet openings employed on the vertical face of the bottommost structural segment. With the fixed non-conventional cap-like base more expense must be taken to ensure proper fit and sealing and is overall undesirable.
As such, there is a continuing and unmet need for a device and method which will remedy the downside of employing concrete and similar cured materials for maintenance holes and liners. The need is unmet for both retrofit and new construction of underground utilities which employ maintenance shafts communicating with below-ground junction points such as sewers and drains in a municipal system.
Such a device and method to overcome the shortcomings of current art, should accommodate construction of junction points for drains and sewers in a conventional fashion so that current workers and equipment may be easily employed. However, such a system and device unlike concrete, should allow for a high degree of customization for the size, number, and angles of intersecting drain conduits with the base component formed. Further, such a system should endeavor to provide manufacturers with a high degree of customization ability so as to empower them with the ability to cheaply and easily form the many new and custom configurations of maintenance hole base platforms to decrease labor costs and increase reliability of the formed intersection. Still further, such a device and system should employ lightweight materials for component formation which are easier to ship and easier to install in the narrow underground confines of maintenance shafts to lessen labor costs and improve the structure. Finally, and most importantly, such a device and system should yield maintenance shafts and bases which are much better at resisting damage from shifts in land and soil supporting it over time.